Polyurethanes are useful in a variety of applications. For example, polyurethane elastomers are used in automotive parts, shoe soles, and other products in which toughness, flexibility, strength, abrasion resistance, and shock-absorbing properties are required. Polyurethanes are also used in coatings and in flexible and rigid foams.
Polyurethanes, in general, are produced by the reaction of a polyisocyanate and a polyol in the presence of a catalyst. The catalyst is typically a low molecular weight tertiary amine such as triethylenediamine.
Polyurethane foams are produced through the reaction of a polyisocyanate with a polyol in the presence of various additives. One class of additives which is particularly effective as blowing agents is the chlorofluorocarbons (CFCs). CFCs vaporize as a result of the reaction exotherm during polymerization and cause the polymerizing mass to form a foam. However, the discovery that CFCs deplete ozone in the stratosphere has resulted in mandates for restricting CFC use. Therefore, more efforts have gone into the development of alternatives to CFCs for forming urethane foams and water blowing has emerged as an important alternative. In this method, blowing occurs from carbon dioxide generated by the reaction of water with the polyisocyanate. Foams can be formed by a one-shot method or by formation of a prepolymer and subsequent reaction of the prepolymer with water in the presence of a catalyst to form the foam. Regardless of the method, a balance is needed between reaction of the isocyanate and the polyol (gelling) and the reaction of the isocyanate with water (blowing) in order to produce a polyurethane foam in which the cells are relatively uniform and the foam has specific properties depending on the anticipated application; for example, rigid foams, semi-rigid foams, and flexible foams.
The ability of the catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a polyurethane foam with specific properties. If a catalyst promotes the blowing reaction to too high a degree, carbon dioxide will be evolved before sufficient reaction of isocyanate with polyol has occurred. The carbon dioxide will bubble out of the formulation, resulting in collapse of the foam and production of a poor quality foam. At the opposite extreme, if a catalyst promotes the gelling reaction too strongly, a substantial portion of the carbon dioxide will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam is produced; characterized by high density, broken or poorly defined cells, or other undesirable features. Frequently, a gelling catalyst and a blowing catalyst are used together to achieve the desired balance of gelling and blowing in the foam.
Tertiary amine catalysts have been used to in the production of polyurethanes. The tertiary amine catalysts accelerate both blowing (reaction of water with isocyanate to generate carbon dioxide) and gelling (reaction of polyol with isocyanate) and have been shown to be effective in balancing the blowing and gelling reactions to produce a desirable product. However, typical tertiary amines used as catalysts for polyurethane production generally have offensive odors and many are highly volatile due to low molecular weight. Release of tertiary amines during polyurethane production may present significant safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Amine catalysts which contain amide functionality have an increase in molecular weight and hydrogen bonding and reduced volatility and odor when compared to related compounds lacking amide functionality. An advantage of the use of compounds having amide functionality in the preparation of polyurethanes is that the amide chemically bonds with the urethane during the polymerization reaction and thus is not released from the finished product. However catalyst structures which contain both amine and amide functionality typically have low to moderate activity and promote both the blowing and gelling reaction to varying extents.
Examples of patents directed to compounds having both tertiary amine and amide functionality are described below:
U.S. Pat. No. 3,073,787 (Krakler, 1963) discloses an improved process for preparing isocyanate foams in which catalysts made from 3-dialkylaminopropionamide and 2-dialkylaminoacetamide are used.
U.S. Pat. No. 4,049,591 (McEntire et al., 1977) discloses a group of 1,3-substituted bis-(N,N,-dimethylaminopropyl)amines as catalysts in reacting polyisocyanate with polyols. The substituted group can be cyano, amide, ester, or ketone.
U.S. Pat. No. 4,248,930 (Haas et al., 1981) discloses several tertiary amines catalysts for the production of polyurethane resins. In the example, a mixture of bis(dimethylamino-n-propyl)amine and N-methyl-N'-(3-formylaminopropyl)piperazine is used to form a PVC/polyurethane-foam laminate.
U.S. Pat. No. 4,548,902 (Hasler et al., 1985) discloses combining a polybasic amino compound, such as 3,3'-{[3-(dimethylamino)propyl]imino}bis-propanamide, with a direct or reactive dyestuff for use in cellulose dyeing applications.
WO 94/01406 (Beller, et al., 1994) discloses a group of chelating agents, such as 3-[3-(N',N'-dimethylaminopropyl)-N-methyl]propionamide, and 3-[3-(dimethylamino)-propyl]propionamide, suitable for producing paramagnetic complexes which can be used as contrast agents in magnetic resonance diagnosis applications.
EP 799,821 (Gerkin, et al., 1997) discloses amine/amide catalysts, such as the following two compounds, ##STR2## for formation of polyurethanes. The catalysts are reported to have low fugitivity due to their reactivity with isocyanates.